JP5508125B2 - Lens device and camera - Google Patents

Description

  The present invention relates to a lens apparatus and a camera.

  A single-lens reflex type camera that has an automatic focus adjustment function (AF system) and includes a photographic lens exchangeable with the camera is often used. In this single-lens reflex camera, a phase difference detection method is often used as a method for detecting the focus adjustment state. In the phase difference detection method, a light flux from a subject that has passed through different exit pupil regions of the photographing lens is imaged on a pair of line sensors, and an image shift between a pair of image signals obtained by photoelectrically converting the subject image. The quantity is obtained by correlation calculation. In the automatic focus adjustment device of a camera, the defocus amount (focus shift amount) of the subject image with respect to the imaging surface is detected by the above-described phase difference detection method or the like before driving the focus lens. Then, the drive amount of the focus lens is calculated according to the detected defocus amount, and the focus lens is driven by the calculated drive amount to focus. Many of them have a servo control function for following the driving of the focus lens with respect to the movement of the subject. When the subject is a moving object, the subject can move even while the focus lens is being driven. For this reason, it is necessary to detect the defocus amount and calculate the focus lens drive amount even while the focus lens is being driven. This is generally referred to as “overlap control” (see Patent Document 1). This overlap control is a method that improves the focus followability with respect to moving objects by correcting the driving amount of the focus lens according to the amount of movement of the moving object, while the focus lens is being driven. Performed multiple times.

In order to realize automatic focus adjustment , it is indispensable to drive and control the focus lens with a motor. A driving mechanism that uses a DC motor as a motor and drives a focus lens via a transmission mechanism such as a gear is disclosed in Patent Document 2. This drive mechanism accelerates to a desired speed (acceleration control), drives at a desired speed (constant speed control), and then decelerates to a speed required to accurately stop at the target position (deceleration control) and stops. . The acceleration control, constant speed control, and deceleration control are all speed control. The rotational speed of the motor or the driving speed of the focus lens is detected at a certain cycle, the detected speed is compared with the desired speed, and if the detected speed is faster than the desired speed, the motor is decelerated . When the detected speed is slower than the desired speed, the motor is accelerated or maintained or changed to the desired speed. In the case of a DC motor, acceleration / deceleration is performed by increasing / decreasing the drive execution voltage or drive execution current.

  There is also an example in which a known step motor is used as a motor for driving the focus lens for the purpose of improving controllability of the focus lens. However, the step motor has a feature that it will step out when it is suddenly accelerated or suddenly stopped. For this reason, in conventional control of a step motor, acceleration and deceleration are performed at a predetermined speed change theoretically or experimentally to prevent step-out of the step motor (Patent Document 3). reference). When the focus lens is driven by a step motor having such characteristics, there are the following problems. As described above, the servo control function (overlap control) in the automatic focus adjustment function corrects the driving amount of the focus lens in accordance with the amount of movement of the moving subject. If correction for reducing the driving amount of the focus lens is performed during the deceleration period of the focus lens, the target focus lens may not be driven due to a miss step caused by step-out of the step motor.

  Patent Document 4 discloses a control method that does not cause a misstep due to a step-out of the step motor even when the drive amount is corrected while the step motor is driven. In this step motor control method, the drive speed is set such that the step motor is gradually lowered as the number of steps decreases with respect to each braking step from the drive state at the preset maximum speed to the stop position. Set the deceleration rate. Then, the set deceleration rate is stored, and the deceleration control of the step motor is performed at the stored deceleration rate. That is, in this step motor control method, even if the stop position of the object driven by the step motor is changed to a position closer to the front than the initial target position, the deceleration control is always performed at the set deceleration rate. Specifically, when the deceleration control is performed with the number of deceleration steps of 10, even if the stop position of the object is changed to the near side from the beginning and the target number of steps is 4, only the number of steps of 10 is set with the set deceleration rate. Decelerate to stop. Then, the object is driven in the opposite direction by 6 steps thereafter, and the object is stopped at the changed stop position.

JP 2002-023046 A Japanese Patent Laid-Open No. 11-221960 Japanese Patent Publication No. 5-38560 Japanese Patent Registration No. 0661590

  In the control of the step motor described in Patent Document 4, the object is stopped after passing through the position to be temporarily stopped, and then the object is driven in the opposite direction to stop at the target stop position. . For this reason, when this control method is applied to the servo control function (overlap control) of the focus lens, a period in which focus is not achieved occurs. The servo control function (overlap control) of the focus lens corrects the drive amount of the focus lens by predicting the amount of movement of the moving subject. However, if the drive time of the focus lens is significantly increased, the movement of the subject and the drive of the focus lens are not compatible. Further, since the driving of the focus lens is different from the movement of the subject, focusing is performed after the focus is once defocused.

  The present invention drives the focus lens according to the corrected drive amount without causing a misstep due to the step-out of the step motor when the drive amount of the focus lens is corrected while the focus lens is driven by the step motor. Objective.

The present invention includes a lens unit including a focus lens, a step motor, and a transmission mechanism that transmits a driving force generated by the step motor to the focus lens to move the focus lens along the optical axis of the lens unit. An operation for positioning the focus lens by the step motor includes an acceleration section and a deceleration section after the acceleration section, and the control unit controls the control. The target drive amount of the focus lens by the step motor for moving the focus lens to the target position along the optical axis is changed during driving of the focus lens, and the remaining drive amount after the change is Smaller than the standard driving amount of the focus lens in the deceleration section of the step motor Ku, in the case where the remaining drive amount after the change is less than the remaining drive amount before the change, on the basis of the driving speed of the step motor at the time of the change and the remaining drive amount after the change, the standard driving amount A deceleration curve relating to the driving speed of the step motor having a deceleration rate larger than a corresponding standard deceleration rate is generated, and the step motor is operated according to the generated deceleration curve.

  According to the present invention, when the driving amount of the focus lens is corrected while the focus lens is driven by the step motor, the focus lens is driven according to the corrected driving amount without causing a misstep due to the step-out of the step motor. Can do.

Block diagram showing the configuration of the camera The figure which shows the drive signal of the step motor Diagram showing acceleration / deceleration characteristics of step motor Step motor control flowchart

  Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 shows a system configuration of an autofocus single-lens reflex camera which is an embodiment of the present invention. The autofocus single-lens reflex camera includes a lens device 1 and a camera body 2 to which the lens device 1 is detachably attached. The lens apparatus 1 is provided with a photographing optical system including a lens unit 3 and a variable magnification lens unit (not shown). The lens unit 3 is a focus lens unit including a focus lens for focusing a subject image and a lens barrel for holding the focus lens. The cam ring 4 includes a cam that is driven to rotate around the optical axis to move the lens unit 3 substantially parallel to the optical axis. The step motor 5 generates a driving force for moving the focus lens along the optical axis of the lens unit 3 and performs an operation for positioning the focus lens. The deceleration mechanism 6 decelerates and transmits the driving force generated by the step motor 5 to the cam ring 4 and rotates the cam ring 4 around the optical axis. The speed reduction mechanism 6 is configured using a plurality of gears. The speed reduction mechanism 6 and the cam ring 4 constitute a driving force transmission mechanism of the step motor 5.

  The step motor 5 is driven when a predetermined drive signal (pattern signal) is input from a driver 7 described later. The driver 7 supplies a current to a coil (not shown) of the step motor 5 based on a pattern signal input from a lens microcomputer 9 described later. The lens microcomputer 9 constitutes a control unit that controls the step motor 5. The driver 7 is composed of, for example, four transistors, and includes a known H bridge circuit for the number of phases of the coil, which can selectively energize the coil in the forward and reverse directions. In the present embodiment, the step motor 5 is a two-phase step motor, and the driver 7 includes at least two H bridge circuits. An example of a predetermined drive signal (pattern signal) input to the driver 7 is shown in FIG. As the drive signal of the two-phase step motor 5, there are known one-phase drive, two-phase drive, 1-2 phase drive, microstep drive, and the like. ). Energization to one coil is set by drive signals A and / A. Specifically, when A = 1 and / A = 0, current flows in the forward direction through the coil, and when A = 0 and / A = 1, current flows in the reverse direction through the coil. Further, energization to the other coil is set by the drive signals B and / B. Specifically, when B = 1 and / B = 0, a current is passed through the coil in the forward direction, and when B = 0 and / B = 1, a current is passed through the coil in the reverse direction. The step motor 5 can be driven (rotated) by switching the energization of each coil with the drive signal shown in FIG. The rotation amount and rotation speed of the step motor 5 can be grasped by the number of patterns of the drive signal (pattern signal) and the pattern change time. However, an encoder (not shown) described later may be provided and detected. An encoder (not shown) includes a pulse plate and a photo interrupter. The pulse plate is provided so as to be able to rotate integrally with a gear near the step motor 5 of the output shaft of the step motor 5 or the speed reduction mechanism 6, and outputs a pulse signal at every predetermined rotation angle To do. The rotation amount and rotation speed of the step motor 5 can be detected by the pulse signal output from the encoder.

  The absolute position sensor 8 for detecting the absolute position (zone) of the lens unit 3 includes a conductive pattern formed on the outer periphery of the cam ring 4 and a detection contact on which the conductive pattern slides. A zone having a predetermined width where the lens unit 3 is located is detected by the absolute position sensor 8, and the absolute position of the lens unit 3 can be detected from the information on the switching of the zone and the rotation amount of the step motor 5. A microcomputer (hereinafter referred to as a lens microcomputer) 9 controls the entire lens apparatus 1 and includes a timer circuit and an A / D circuit in addition to an arithmetic circuit, a communication circuit, and an internal memory. A microcomputer (hereinafter referred to as a camera microcomputer) 10 mounted on the camera body 2 side includes an arithmetic circuit, a communication circuit, an internal memory, a timer circuit, an A / D circuit, and the like in the same manner as the lens microcomputer 9. Governs the overall control of The contact unit 11 for performing serial communication with the camera microcomputer 10 has a plurality of contacts. The contact unit 11 also has a contact for supplying power to the lens apparatus 1 from a battery (not shown) provided in the camera body 2. The camera body 2 includes a detector (focus detection unit) that detects the defocus amount of the lens unit 3 including the focus lens. The focus detection unit 12 includes a pair of CCD line sensors (not shown) and a focus detection optical system that forms an image of light incident from the photographing optical system on the pair of CCD line sensors. The focus detection unit 12 detects the defocus amount of the lens unit 3 from the deviation between the two image signals imaged on the pair of CCD line sensors. There are many other functions in the camera body 2, but the description thereof is omitted here.

  Hereinafter, the operation of the camera will be described. When the camera microcomputer 10 detects that the lens apparatus 1 is mounted by a mounting sensor (not shown), the camera microcomputer 10 tries to communicate with the lens microcomputer 9 through the contact unit 11. Through this communication, the camera microcomputer 10 confirms that the lens apparatus 1 has been normally mounted, and the lens microcomputer 9 and the camera microcomputer 10 each perform a predetermined initialization operation. Next, when an instruction to start autofocus is input to the camera microcomputer 10 by the user's switch operation, the camera microcomputer 10 operates the focus detection unit 12 to detect the defocus amount of the lens unit 3. The camera microcomputer 10 calculates a target driving amount A (including the driving direction) of the focus lens necessary for obtaining the focus based on the detected defocus amount, and passes the target driving to the lens microcomputer 9 through the contact unit 11. Send quantity A information. When the information about the target drive amount A is transmitted from the camera microcomputer 10, the lens microcomputer 9 starts driving the focus lens by the step motor 5 described later. Information on the target drive amount A from the camera microcomputer 10 is stored in the internal memory of the lens microcomputer 9. Thereafter, the lens microcomputer 9 stores information representing the driving amount and driving speed of the focus lens from the driving information of the step motor 5 in the internal memory of the lens microcomputer 9.

  After the lens microcomputer 9 starts driving the focus lens, the lens microcomputer 9 performs acceleration processing in the acceleration section, and information indicating that overlap control is possible when the focus lens drive speed reaches the target speed and constant speed control is performed. Is transmitted to the camera microcomputer 10. After receiving this information, the camera microcomputer 10 starts the above-described overlap control. The camera microcomputer 10 transmits a communication request for information representing the current driving amount to the lens microcomputer 9 in order to know the current position of the focus lens. In response to this, the lens microcomputer 9 transmits drive amount information stored in the internal memory of the lens microcomputer 9 in response to the communication request. When confirming that the drive amount information has been transmitted, the camera microcomputer 10 operates the focus detection unit 12 to detect the defocus amount of the lens unit 3. When the detection of the defocus amount is completed, the camera microcomputer 10 transmits a communication request for driving amount information to the lens microcomputer 9 in order to know the current position of the focus lens again. The lens microcomputer 9 transmits drive amount information to the camera microcomputer 10 in response to the communication request.

  When the camera microcomputer 10 confirms that the drive amount information has been transmitted, the camera microcomputer 10 calculates the stop position of the focus lens for obtaining focus. This stop position is calculated using the driving amount information of the focus lens acquired before and after detecting the defocus amount and optical information (sensitivity, focus error information, etc.) acquired from the lens microcomputer 9. When the calculation of the stop position of the focus lens is completed, the camera microcomputer 10 sets a new target drive amount B of the focus lens that focuses on the subject. The camera microcomputer 10 transmits a new target drive amount B to the lens microcomputer 9 as an overlap drive amount. The lens microcomputer 9 performs a correction process to be described later so as to drive the focus lens by the received new target drive amount B. After that, the camera microcomputer 10 performs the photographing process, but the description is omitted here.

  Next, a method for controlling the step motor 5 by the lens microcomputer 9 accompanying the above overlap control will be described with reference to FIGS. First, when there is transmission of information on the target driving amount A for moving the focus lens to the target position along the optical axis from the camera microcomputer 10, the lens microcomputer 9 performs initial processing described later. The lens microcomputer 9 stores the target drive amount A as a total drive amount (SCT) by the initial process. In the present embodiment, this target drive amount A (total drive amount) is 100, that is, SCT = 100. Here, the target drive amount A (total drive amount) is expressed by the number of steps of the step motor 5. Also, the number of acceleration steps SCA in the acceleration section is set. The number of acceleration steps SCA is the number of steps necessary to reach the target drive speed VP. In this embodiment, the number of acceleration steps is 10, that is, SCA = 10. Also, the standard deceleration step number SCD in the deceleration section after the acceleration section and the constant speed section is set. The standard deceleration step number SCD in the deceleration section is the number of steps of the step motor 5 corresponding to the standard driving amount of the focus lens in the deceleration section of the step motor 5. In this embodiment, the standard number of deceleration steps is 20, that is, SCD = 20. The standard deceleration step number SCD is a step number with a margin in advance with respect to the number of steps that the step motor 5 can reach without stopping. FIG. 3 shows the acceleration / deceleration characteristics of the step motor 5 set in the present embodiment. The horizontal axis indicates the number of steps, and the vertical axis indicates the driving speed of the focus lens by the step motor 5. D1 indicates a deceleration curve having the maximum deceleration rate within a range in which the step motor 5 can stop without stepping out of the target drive speed VP. D2 indicates a standard deceleration curve having a standard deceleration rate based on the standard deceleration step number SCD set in the initial process described above. A step counter (SC) is provided to manage the number of steps of the step motor 5, and SC = 0. Also, an initial energization pattern of the step motor 5 is output, and a timer interrupt process for the next energization pattern change process is performed. In the present embodiment, the energization pattern of the step motor 5 is changed by timer interruption processing. That is, by setting a timer value until the next energization pattern change, an interrupt process occurs when the timer reaches that value, and the energization pattern change process of the step motor 5 is performed.

  FIG. 4 is a flowchart from after the above-described initial processing until the driving of the step motor 5 is completed. This process is the above-described timer interruption process and is performed at the timing when the energization pattern of the step motor 5 is changed. In S1, the lens microcomputer 9 confirms whether or not the target driving amount of the focus lens by the step motor 5 for moving the focus lens to the target position has been changed during driving of the focus lens. If changed, the process proceeds to S2. If not changed, the process proceeds to S7. When the target drive amount B is set to the initial target drive amount A by the above-described overlap control, the process proceeds to S2. In S2, the lens microcomputer 9 checks whether or not the remaining drive step number (SCT-SC) before the change of the step motor 5 is larger than the standard deceleration step number SCD. The number of remaining drive steps (SCT−SC) before the change of the step motor 5 corresponds to the remaining drive amount before the focus lens is changed by the step motor 5. If SCT−SC ≧ SCD, the lens microcomputer 9 determines that constant speed processing is in progress, and proceeds to S3. If SCT-SC <SCD, the lens microcomputer 9 determines that deceleration processing is being performed, and proceeds to S4. In S3, the lens microcomputer 9 checks whether or not the target drive step number (new SCT) changed during the constant speed process is larger than the standard deceleration step number SCD. The target drive step number (new SCT) after the change corresponds to the remaining drive amount after the focus lens is changed by the step motor 5. When the new SCT ≧ SCD, it is not necessary to change the deceleration curve of the deceleration process from the standard deceleration curve, so the process proceeds to S6. If the new SCT <SCD, it is necessary to change the deceleration curve of the deceleration process from the standard deceleration curve, so the process proceeds to S5.

  In S4, the lens microcomputer 9 checks whether or not the changed target drive step number (new SCT) changed during the deceleration process is larger than the remaining drive step number (SCT-SC) before the change. When the new SCT ≧ SCT−SC, it is not necessary to change the deceleration curve of the deceleration process from the standard deceleration curve, so the process proceeds to S6. When the new SCT <SCT-SC, the deceleration curve of the deceleration process needs to be changed from the standard deceleration curve, and the process proceeds to S5. In S5, the lens microcomputer 9 performs a change process for changing the deceleration curve of the deceleration process from the standard deceleration curve. Specifically, a deceleration curve having a new deceleration rate is generated from the current drive speed V0 and the number of remaining drive steps after the change (new SCT). Details of the method of generating the deceleration curve will be described later. In S6, the lens microcomputer 9 stores the changed target drive step number (new SCT) as a total drive amount (SCT). In S7, the lens microcomputer 9 confirms whether or not the step counter (SC) matches the total drive amount (SCT). If SC = SCT, it is determined that the target drive amount has been driven, and the process proceeds to S8 to perform stop processing. If SC ≠ SCT, the process proceeds to S9. In S8, the lens microcomputer 9 ends the energization and ends the timer interrupt process without setting the timer value until the next energization pattern change. This process ends the driving of the step motor 5. In step S9, the step counter (SC) is incremented by 1, and the process proceeds to step S10. In S10, the lens microcomputer 9 checks whether or not the step counter (SC) is smaller than the acceleration step number (SCA). In the case of SC <SCA, it is determined that it is an acceleration section, and the process proceeds to S12 to perform acceleration processing. If SC ≧ SCA, the process proceeds to S11. In S11, the lens microcomputer 9 checks whether or not the changed remaining drive step number (SCT-SC) is larger than the standard deceleration step number SCD. When SCT−SC ≧ SCD, it is determined that the constant speed process is being performed, and the process proceeds to S13. If SCT-SC <SCD, it is determined that deceleration processing is in progress and the process proceeds to S14. In S12, the lens microcomputer 9 performs acceleration processing. Specifically, the number of steps and driving speed data matched to the acceleration curve indicated by A1 in FIG. 3 are set in advance, and the driving speed data is extracted from the current step counter (SC) until the next energization pattern change. Set the timer value and end the timer interrupt process. In S13, the lens microcomputer 9 performs constant speed processing. Specifically, the timer value until the next energization pattern change is set in the driving speed data indicated by VP in FIG. 3, and the timer interruption process is terminated. In S14, the lens microcomputer 9 performs a deceleration process. Specifically, the number of steps and drive speed data that match the deceleration curve indicated by D2 or D3 in Fig. 3 are set in advance, the drive speed data is extracted from the current step counter (SC), and the next energization pattern change Set the timer value up to and end the timer interrupt process.

  Although the step motor 5 can be driven by the operation of this flowchart, the operation when the target drive amount is changed during the drive, which is a feature of the present invention, will be described. As described above, the standard deceleration step number SCD is set to 20 from the initial target drive amount A, and the deceleration curve is set to D2. Thereafter, the target drive amount B was updated by overlap control while the step motor 5 was being driven. A method of changing the deceleration curve will be described by taking as an example a case where the target drive amount B is set to 10 and the target drive amount is updated at a position during P1 deceleration processing (the number of remaining drive steps = 15) in FIG. If the deceleration curve is not changed from the standard deceleration curve D1 due to the update of the target drive amount, the remaining amount of the drive step has been changed to 10, so that the position is 5 before the original target drive amount (P2) In this case, the driving is ended. In this case, since the energization is stopped without being able to decelerate to a sufficient speed, the step motor 5 may cause a step error due to the step-out, and there is a possibility that the stop position cannot be sufficiently secured. On the other hand, in the present embodiment, the lens microcomputer 9 performs a deceleration curve changing process in the deceleration process of S5 as follows. The lens microcomputer 9 determines a deceleration rate larger than the standard deceleration rate of the standard deceleration curve D1 from the drive speed (V0) at the time P1 of the change, the target drive speed (V1) at the time of stop, and the remaining drive step number (new SCT). Generate a deceleration curve D3. The deceleration curve D3 is gentler than the deceleration curve D1 having a maximum deceleration rate in a range where at least the step motor 5 can stop without stepping out. That is, the deceleration rate of the deceleration curve D3 is a deceleration rate within a range where the step motor 5 can be stopped without stepping out. Accordingly, the deceleration curve can be changed along with the update of the target drive amount to decelerate to a sufficient speed and stop energization, and sufficient stop position accuracy can be ensured.

  If the change amount of the target drive amount is small and the deceleration curve obtained by the above-described deceleration curve changing method becomes steeper than D1, the deceleration curve is set with the slope of D1 as the limit. In this embodiment, the relationship between the number of steps and the driving speed is described in a substantially linear relationship with respect to the deceleration curve to be changed. However, the relationship can be such that the driving speed changes more gradually as the remaining driving step amount decreases. . In setting the deceleration curve to be changed and set, the target drive speed V1 at the time of stop in FIG. 3 is the same as the target drive speed at the time of stop in the standard deceleration curve, but may be a different target drive speed.

According to the present embodiment, when the target driving amount of the focus lens is changed while the step motor 5 is being driven, the step motor 5 can be controlled so that a misstep due to the step-out of the step motor 5 does not occur. Further, in the servo control function (overlap control) in the dynamic focus adjustment function, the movement of the focus lens can be matched with the movement of the subject. The present invention can be mounted on a photographing apparatus such as a single-lens reflex camera, its interchangeable lens, a compact camera, and a video camera.

Claims (4)

A lens unit including a focus lens; a step motor; a transmission mechanism that transmits a driving force generated by the step motor to the focus lens to move the focus lens along an optical axis of the lens unit; and the step motor. A lens device comprising a control unit for controlling
The operation for positioning the focus lens by the step motor includes an acceleration section and a deceleration section after the acceleration section,
The control unit changes a target drive amount of the focus lens by the step motor for moving the focus lens to a target position along the optical axis while the focus lens is being driven, and the remaining drive after the change When the amount is smaller than the standard drive amount of the focus lens in the deceleration section of the step motor and the remaining drive amount after change is less than the remaining drive amount before change, the remaining drive amount after change and the time of change Based on the driving speed of the step motor in step (b), a deceleration curve relating to the driving speed of the step motor having a deceleration rate larger than a standard deceleration rate corresponding to the standard driving amount is generated, and according to the generated deceleration curve Operate the step motor,
A lens device.   The lens apparatus according to claim 1, wherein the deceleration rate of the deceleration curve is a deceleration rate within a range in which the step motor can be stopped without being stepped out. A lens unit including a focus lens; a step motor; a transmission mechanism that transmits a driving force generated by the step motor to the focus lens to move the focus lens along an optical axis of the lens unit; and the lens unit A camera that includes a detector that detects the amount of defocus, and a controller that controls the step motor,
The operation for positioning the focus lens by the step motor includes an acceleration section and a deceleration section after the acceleration section,
The control unit is configured to detect a defocus in which a target driving amount of the focus lens by the step motor for moving the focus lens to a target position along the optical axis is detected by the detector during driving of the focus lens. When the remaining drive amount after the change is smaller than the standard drive amount of the focus lens in the deceleration section of the step motor and the remaining drive amount after the change is less than the remaining drive amount before the change. Deceleration related to the driving speed of the step motor having a deceleration rate larger than the standard deceleration rate corresponding to the standard driving amount based on the changed remaining driving amount and the driving speed of the step motor at the time of the change Generating a curve and operating the step motor according to the generated deceleration curve;
A camera characterized by that.   The camera according to claim 3, wherein the deceleration rate of the deceleration curve is a deceleration rate within a range in which the step motor can be stopped without being stepped out.

Images